The present invention relates generally to improvements in field transplant systems and methods and components thereof, wherein polymerized soil plugs are formed and seeded, the seeds germinated and grown to provide plants that are of field transplant size, and the plants being thereafter automatically planted in a field.
The ideal time to transplant seedlings or plants is when the plants are still quite small; for example, in the case of lettuce seedlings, the ideal transplant time is after the first true leaf has partially expanded, this being approximately twelve to fifteen days after planting; in the case of celery, the ideal transplant time is after the first true leaf has partially expanded, this being approximately twenty-five to thirty days after planting. Prior transplant systems have required plants to be substantially greater in size, the typical commercial head lettuce transplant having grown for twenty-five to forty days in a greenhouse after planting, and the typical commercial celery transplant having grown fifty to seventy-five days in a greenhouse after planting.
Transplanting the seedling when it is still quite small has several advantages: (1) the root system is less fully differentiated so that more roots on the seedling are hair roots and water absorbing; (2) the top or leaf of the plant does not put too great a water demand on the root system, i.e., a water demand beyond the capacity of the root system to provide water; (3) the growth system of the plant has not yet been physiologically modified so as to require the sophisticated greenhouse growing conditions; and (4) if the transplant is put in the field soil at an angle of even 45.degree. with respect to the vertical, the stalk will straighten up and grow upright without deforming the mature plant.
Ideally the seeds for field transplant production are subjected to uniform germination conditions, and more uniform germination of seeds is obtained if: (1) there is good contact between the seed and the soil surrounding it; (2) there is ready access by the seed to the oxygen in the air since the sprouting seed requires oxygen for respiration and its normal growth processes; and (3) water is supplied directly to the seed with excess water draining away from the seed, but the seed being maintained continually in a moist condition. Prior commercial transplant systems have not provided these ideal germination conditions since they have required layers of soil to be applied over the seeds, and there has been no special controlled provisions made for aeration and watering of the seed during germination.
One form of prior field transplanting system, known as the "Speedling" system, utilizes a seedling flat as illustrated in the Todd U.S. Pat. No. 3,667,159 granted June 6, 1972. The flat of the Todd patent is formed of plastic and includes a number of downwardly tapered soil cells in which individual seedlings are started. The soil utilized is frequently a mixture of peat and vermiculite because such a mixture is readily handled in conventional mixing and dispensing apparatus. After seeding, the flat is held in a greenhouse until the seedlings are the size required for transplanting, after which the flat is taken to the field where the seedlings are to be transplanted. The seedlings are manually removed from the flat, and in the process, 25% to 60% of the soil falls from the roots so that essentially a bare root seedling is manually fed to a transplanter which grasps the seedling by the stalk and moves it to the transplanted position in the soil.
Since the seedling must be handled by its stalk during the transplanting operation in accordance with the "Speedling" system, the seedling must be of substantial size, and in the case of lettuce, the seedling has been grown for twenty-five to fifty days in the greenhouse, twenty-eight days being typical, and in the case of celery, has been grown fifty to seventy-five days in the greenhouse, sixty days being typical. As a consequence, the seedlings are well past the ideal transplant stage which is about fifteen days in greenhouse cultivation for lettuce and about thirty in greenhouse cultivation for celery. Despite the greater size of the plants in the "Speedling" system, there is substantial "transplanting shock" as evidenced by the fact that despite the usual twenty-eight days greenhouse growth of the seedling prior to transplant, in comparison to direct seeding, there is only an advance of ten to fifteen days in the harvest date, thus showing that on an average there is a fifteen day loss from "transplanting shock". Transplanting shock results from a substantial loss of the water absorbing hair roots when 25% to 60% of the soil falls from the roots during the manual feeding of the seedling to the transplanter. In addition, the leaf development on a twenty-eight day lettuce seedling is large compared to the resultant root capacity after transplanting so that the plants must be quickly watered or a substantial loss or mortality will result. Further it is clear that the twenty-eight day lettuce seedlings have been physiologically modified due to their long holding time under greenhouse growing conditions, whereby there is the resultant shock when the seedling is exposed to the normally more rigorous field conditions. Furthermore, if the twenty-eight day lettuce seedling is not planted with the stalk extending essentially upwardly, there may develope a deformation of the mature plant which renders the resultant head of lettuce less valuable in the market place.
Another prior transplanting system is illustrated in the Huang et al. U.S. Pat. No. 3,446,164 granted May 27, 1969 and the Huang U.S. Pat. No. 3,712,252 granted Jan. 23, 1973. These patents disclose a tobacco transplant system wherein tobacco seedlings are grown in a compartmentalized tray having a plurality of cells therein, each cell containing a quantity of soil in which the seedling is grown under greenhouse conditions. The soil masses held together by the roots of the seedling are then planted using the transplanter of U.S. Pat. No. 3,446,164 which utilizes vacuum to pull the soil masses from a tray thereof and deposits the same in an opening formed in the soil.
Since the Huang et al. system relies upon a well developed root system to hold the soil masses together during transplanting, again the transplant seedling has a size well beyond the ideal for transplanting. As a result, there may be substantial "transplanting shock". This is caused by a combination of factors including the fact that the top of the plant is large compared to the root system, whereby there is substantial tendency to wilt until the root system is reestablished. Further, the more mature plant has had its growth system physiologically modified in response to the non-taxing greenhouse holding conditions from which it requires several days for the plant to adjust to the more rigorous field conditions usually encountered. Furthermore, since the plant is more mature, it must be placed essentially upright in the soil, otherwise the resultant mature plant is deformed and of less economic value.
Basically the problem with using more mature transplants is that they are too much differentiated to readily adapt to differing field conditions during their subsequent development.
Additional problems were encountered in the Huang et al. system in the operation of the automatic transplanter forming a part thereof. The velocity of the plant in the tube leading from the support plate to the furrow is dependent upon the integrity of the soil plug, which in turn is dependent upon the extent of the roots of the plant in the soil plug to hold the same together. Substantial difficulty has been encountered in that the roots of plants of ideal size for transplant are not sufficient to hold the soil plug together and thus provide a uniform velocity of the plant in the aforementioned tube. In an effort to further stabilize the soil plug, larger plants are provided which in turn necessitates a larger top to root ratio and a larger plant top. Since the plant top must pass through the cavity in the support tray, difficulties are inevitable.